Studs, bolts and rods may be tensioned in order to provide a secure mechanical connection between structural members, such as, for example, a pair of opposing flanges on a piece of machinery. The tensioning of a stud or bolt is typically accomplished by a tensioning system or device that applies an axially-directed force to the stud in a direction away from the structural member. The tensioning system generally includes a mechanism for gripping the stud and a load cell. An axially-directed force is applied by the load cell to the gripping mechanism. The gripping means transfers the force to the stud, and thereby axially tensions or stretches the stud. The stud is then mechanically retained in its stretched or tensioned position by, for example, a nut that threadingly engages external threads formed on the stud and which is tightened down to engage the flange.
Some conventional tensioning systems utilize mechanical load cells, whereas other tensioning systems use hydraulic load cells. Mechanical load cells convert mechanical pressure or force to the axial tensioning force, whereas hydraulic load cells convert hydraulic pressure to the axial tensioning force. Tensioning systems may be configured as either internal gripping, external gripping or integrated tensioning systems where the tensioner is integrated with the fastener.
Consistent with the description provide above, hydraulic tensioning systems typically include a hydraulic cylinder with a pulling feature, such as a puller nut, that attaches to the stud, and a reacting foot that presses against an exposed surface of the flange. An example of an existing hydraulic tensioning system can been seen in FIGS. 1A and 1B, which will be described in more detail below. While existing hydraulic tensioning systems may be effective in most applications, they suffer from a number of drawbacks and deficiencies. For example, existing hydraulic tensioning systems, such as the example provided in FIGS. 1A and 1B, include a hole or passage having an inner diameter that provides a space along the inner axis to allow the stud to be disposed therein so that the stud can be engaged with the tensioning system. However, one result of including such a hole or passage is a reduction of the hydraulic pressure area for a given tension system diameter. To account for this reduction in hydraulic pressure area, either tension load must be sacrificed, the tensioning system must be larger in diameter, the tensioning system must be longer to include additional cylinders, or the tensioning system must be designed for higher operating pressures, any one or combination of which may be undesirable options.
There are also instances in which a hydraulic tensioning system malfunctions or breaks when being used to apply an axial tension force on a stud. Given the high pressures that are used to apply the tension force on the stud, a malfunction or breakage of the tensioning system could potentially cause one or more of the parts of the tensioning system or the stud to be projected toward a user. Currently, there is no adequate mechanism for capturing these broken parts, thereby increasing the risk of a user being injured in such an event.
As such, there is a need for an improved hydraulic tensioning system that overcomes the drawbacks and deficiencies mentioned above. The present invention fulfills these and other needs.